update proxyType values to match w3c spec

[titusfortner]

Description

• Update comments; there are no defaults in spec (https://w3c.github.io/webdriver/#ref-for-dfn-own-properties-2)
• Remove outdated Firefox integer values
• Remove invalid reserved option
• Require proxyType to be set before using

Motivation and Context

Making the libraries consistent between languages and updating to match w3c behavior.

Notes

• Looking at the JS code, I don't think it needs any changes to match.
• I'm not sure how much of this can/should be marked deprecated instead of just making these changes to conform to the spec.
• I was going to remove "Unspecified" as an enum, but it makes sense to keep it I think in Java & .NET because strict, but not as much in Python, so removed to match Ruby & JS implementations

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (7cbfdbd) 57.99% compared to head (76f7054) 58.12%.
Report is 3 commits behind head on trunk.

❗ Current head 76f7054 differs from pull request most recent head 04c0159. Consider uploading reports for the commit 04c0159 to get more accurate results

Files	Patch %	Lines
py/selenium/webdriver/common/proxy.py	66.66%	3 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##            trunk   #13285      +/-   ##
==========================================
+ Coverage   57.99%   58.12%   +0.12%     
==========================================
  Files          88       88              
  Lines        5338     5335       -3     
  Branches      224      224              
==========================================
+ Hits         3096     3101       +5     
+ Misses       2018     2010       -8     
  Partials      224      224              

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[titusfortner]

I feel like I read something completely different every time I look at the spec:

Otherwise
Set a property of capabilities with name "proxy" and a value that is a new JSON Object.

Grid is deserializing the empty Proxy and failing, so I need to remove the errors I'm throwing here. 😂

[diemol]

@titusfortner what is left to do here?